Vehicle vision system with enhanced low light capabilities

ABSTRACT

A vehicular multi-camera vision system includes a plurality of cameras and a control having an image processor operable to process image data captured by the cameras. The control is operable to control a display intensity of video images displayed by a video display screen. Responsive to a determination of a reduction in exterior ambient light level within the field of view of at least one of the cameras, the control holds display intensity of video images displayed by the video display screen to within 15 percent of the display intensity that was displayed before the determination of the reduction in exterior ambient light level by (a) adjusting an exposure time for image data capture by at least some of the cameras and by (b) adjusting a frame rate of image data capture by at least one of the cameras and/or) adjusting a gain of at least one of the cameras.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/290,028, filed May 29, 2014, now U.S. Pat. No. 9,800,794,which is related to U.S. provisional application, Ser. No. 61/830,375,filed Jun. 3, 2013, which is hereby incorporated herein by reference inits entirety.

FIELD OF THE INVENTION

The present invention relates generally to a vehicle vision system for avehicle and, more particularly, to a vehicle vision system that utilizesone or more cameras at a vehicle.

BACKGROUND OF THE INVENTION

Use of imaging sensors in vehicle imaging systems is common and known.

Examples of such known systems are described in U.S. Pat. Nos.5,949,331; 5,670,935 and/or 5,550,677, which are hereby incorporatedherein by reference in their entireties.

SUMMARY OF THE INVENTION

The present invention provides a vision system or imaging system for avehicle that utilizes one or more cameras (preferably one or more CMOScameras) to capture image data representative of images exterior of thevehicle, and provides the communication/data signals, including cameradata or captured image data, that may be displayed at a display screenthat is viewable by the driver of the vehicle, such as when the driveris backing up the vehicle, and that may be processed and, responsive tosuch image processing, the system may detect an object at or near thevehicle and in the path of travel of the vehicle, such as when thevehicle is backing up. The vision system may be operable to display asurround view or bird's eye view of the environment at or around or atleast partially surrounding the subject or equipped vehicle, and thedisplayed image may include a displayed image representation of thesubject vehicle. The present invention also provides enhanced low lightvision capabilities to enhance detection of objects in low lightconditions. The system may adjust one or more parameters, such asexposure period and/or frame rate to provide enhanced camera vision ormachine vision in low lighting conditions, while providing a generallyconstant display output or the like.

According to an aspect of the present invention, a vision system of avehicle includes a camera and a control. The camera is disposed at avehicle and has a field of view exterior of the vehicle, such asrearwardly of the vehicle or forwardly of the vehicle. The cameraincludes a pixelated imaging array having a plurality of photosensingelements. The control has an image processor operable to process imagedata captured by the camera. Responsive to a determination of a reducedambient light level or reduction in ambient light level at the imagedscene, the control is operable to adjust at least one of (i) an exposuretime for image capture by the camera and (ii) a frame rate of imagecapture by the camera. Optionally, for example, responsive to adetermination of a reduction in ambient light level at the imaged scene,the control may adjust the exposure time to a longer exposure time andmay adjust the frame rate to a slower frame rate.

These and other objects, advantages, purposes and features of thepresent invention will become apparent upon review of the followingspecification in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a vehicle with a vision system thatincorporates cameras in accordance with the present invention;

FIG. 2 is a graph showing various lighting conditions and the gainadjustment to achieve a relatively constant illumination reproduction asthe lighting conditions darken;

FIG. 3 is a graph showing the relationship between source illuminationand the overall illumination gain of the system of the presentinvention;

FIG. 4 is a block diagram of the system of the present invention,showing the system utilizing a look up table to determine theappropriate adjustments in response to a determined or detected sourceillumination;

FIGS. 5-16 are images showing lab testing of the vision system of thepresent invention in various lighting conditions; and

FIGS. 17-22 are images showing actual vehicle testing of the presentinvention in various lighting conditions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A vehicle vision system and/or driver assist system and/or objectdetection system and/or alert system operates to capture images exteriorof the vehicle and may process the captured image data to display imagesand to detect objects at or near the vehicle and in the predicted pathof the vehicle, such as to assist a driver of the vehicle in maneuveringthe vehicle in a rearward direction. The vision system includes an imageprocessor or image processing system that is operable to receive imagedata from one or more cameras and provide an output to a display devicefor displaying images representative of the captured image data.Optionally, the vision system may provide a top down or bird's eye orsurround view display and may provide a displayed image that isrepresentative of the subject vehicle, and optionally with the displayedimage being customized to at least partially correspond to the actualsubject vehicle.

Referring now to the drawings and the illustrative embodiments depictedtherein, a vehicle 10 includes an imaging system or vision system 12that includes at least one exterior facing imaging sensor or camera,such as a rearward facing imaging sensor or camera 14 a (and the systemmay optionally include multiple exterior facing imaging sensors orcameras, such as a forwardly facing camera 14 b at the front (or at thewindshield) of the vehicle, and a sidewardly/rearwardly facing camera 14c, 14 d at respective sides of the vehicle), which captures imagesexterior of the vehicle, with the camera having a lens for focusingimages at or onto an imaging array or imaging plane or imager of thecamera (FIG. 1). The vision system 12 includes a control or electroniccontrol unit (ECU) or processor 18 that is operable to process imagedata captured by the cameras and may provide displayed images at adisplay device 16 for viewing by the driver of the vehicle (althoughshown in FIG. 1 as being part of or incorporated in or at an interiorrearview mirror assembly 19 of the vehicle, the control and/or thedisplay device may be disposed elsewhere at or in the vehicle). The datatransfer or signal communication from the camera to the ECU may compriseany suitable data or communication link, such as a vehicle network busor the like of the equipped vehicle.

As shown in FIG. 2, curve 21 represents real world lighting/illuminationconditions. The human eye is very capable in adapting to lightingconditions. Outside at summer daylight the illumination is differentthan at night having, for example, one candle as illumination. The humaneye can perceive at both conditions.

Electronically cameras have a limited illumination perception orperceivability range, especially in dark or low lighting conditionswhere the perceivability of the electronic photosensing pixels of thecamera is at its borderline or threshold limits of operation. To makecameras see (at least something) also in darkness, the incoming lighthas to be collected physically, especially optically with enhancedlenses or electronically via image processing of captured image data.The camera can either collect more photons on the pixels by lengtheningthe exposure time or by further amplifying the signals of the pixels.Theoretically, the signal amplification (analog and digital gain) andexposure time is interchangeable. However, by increasing theamplification, the pixel noise also becomes amplified, which is whyamplifying should be limited or avoided.

By extending the exposure time, the captured images motion blurringincreases.

The cameras algorithms are capable to compensate the motion blurring toa certain extent (motion compensation). The exposure time cannot exceedthe time distance between two frames. The time distance between twoframes plus some overhead is the natural limit to which the exposuretime may be extended for collecting more light (such as for counteringon low environmental light conditions). When cutting or reducing thenumber of frames taken within a second by about half, such as, forexample, from 30 fps to 15 fps, the exposure time may be doubled. Thus,the night view capability can be doubled under the cost of increasedmotion blurring and increased pixel noise when turning the amplification(gain) to maximum.

As shown in FIG. 2, curve 22 is the overall amplification (analog gain,digital gain, exposure time), and curve 20 is the illuminationreproduction on a target system. The target may comprise a machinevision system (having an image processor that processes image datacaptured by the camera) or a display (that displays images derived fromimages or image data captured by the camera). It is assumed here that4000 may be the lowest borderline at which a scene is conceivable on thedisplay. Above 4000, the display reproduces the captured illuminationlevel truly (1:1), but when the captured illumination drops under 4000,the target system starts to add (gain) to the truly capturedillumination level (this is done by the camera and not by the display,since the camera knows the minimum output level by parameter). Thedistance between 20 and 21 is closed by the factor of 22. In FIG. 2, thevarious lighting conditions are shown as bright sunlight conditions 23,with a strong source illumination (natural illumination in front of thecamera), daylight cloudy conditions 24, with a high source illumination,dark conditions 25, such as like at moonlight or street lamp light, withlow source illumination, and very dark conditions 26, such as a cloudynight, with very low source illumination.

The present invention provides a light control algorithm with improvedlow light performance, and the algorithm may achieve this via reducingthe frame rate, such as from the typical 30 frames per second to about15 frames per second, for example. The aim of the loop control of thealgorithm is to keep the displayed illumination at a constant mediumlevel (so it is not too bright and not too dark) when the sourceillumination is more and more reducing or diminishing. The presentinvention utilizes or adjusts the frame rate (so that the frame rate isa variable) to enhance collection of more light in reduced lightingconditions.

As shown in FIG. 4, the system has four variables to control theillumination:

-   -   Frame rate (30 frames/sec, 15 frames/sec, . . . ) f    -   Digital gain ( 1/32, 1/64, . . . ) d    -   Analog gain (x1, x2, x4, x8, . . . ) a    -   Exposure (time expressed in n lines) e        The illumination level is a product of all four factors (f, d, a        and e). When one changes, one or more others of the factors have        to counter change to keep the illumination level or brightness        constant or substantially constant.

When the illumination of a to-be-captured scene is diminishing, theexposure time may be controlled longer. The exposure time is maximumlylimited to the time one frame takes (or fractions of one frame in thecase of using high definition resolution (HDR) imagers, which may takeshort and long frames consecutively (such as done by imagerscommercially available from Aptina of San Jose, Calif.) or at the sametime (such as done by imagers commercially available from OmnivisionTechnologies of Santa Clara, Calif.)). When the exposure time is at itslongest end, the gain will have to be increased. With the gain increase,the noise level also increases. This is why exposure adjustment orcontrol is preferred. Because the digital gain is more rough, the analoggain may be tuned first before the digital. When the gain end exposureis on its end due to further diminished lighting conditions, the framerate may be shifted or adjusted, such as from 30 fps to 15 frames persecond, which enables the exposure to be longer (such as about double)since every frame lasts longer. As can be seen in FIG. 3, when the framerate is adjusted or switched the other values have to be switched off(or reduced).

The present invention preferably provides the adjustments or switcheswithout causing brightness flicker or long term waves. The system'scontrol may employ an index value pre control rather than waiting forthe illumination error to be fed back to the input. Because the numberof control states is limited to e×a×d×f and some behaviors inillumination are not fully linear and by that not easy to expressmathematically, a look up table containing all illumination to controlstate relations may come into use in practice. It's a relation becauseoften different combinations may be possible to use for achieving onedesired overall gain factor.

Thus, the present invention provides a vision system with enhancedperformance in low lighting conditions. The system may control or adjustthe frame rate of image capture of the camera or cameras to enablelonger exposure times, such as by reducing the frame rate from around 30fps to about 15 fps. The system may decouple the color and luminanceprocessing to improve detail visibility. FIGS. 5-16 illustrate labtesting of the vision system of the present invention in variouslighting conditions, with FIGS. 5, 7, 9, 11, 13 and 15 showing thecaptured images when captured under normal or conventional image capturemeans, while FIGS. 6, 8, 10, 12, 14 and 16 show the captured images whenthe frame rate and/or other parameters are adjusted in accordance withthe present invention. FIGS. 17-22 illustrate actual vehicle testing ofthe present invention in various lighting conditions, with FIGS. 17, 19and 21 showing the captured images when captured under normal orconventional image capture means, while FIGS. 18, 20 and 22 show thecaptured images when the frame rate and/or other parameters are adjustedin accordance with the present invention. As can be seen with referenceto FIGS. 5-22, the present invention substantially improves scenevisibility in low lighting conditions. The system may also utilize analgorithm that reduces noise for non-moving objects in the sceneencompassed by the camera.

In accordance with the present invention, the display illumination level(i.e., the display intensity) of displayed video images (commonlyexpressed in candelas per square meter), as viewed by the driver who isviewing the in-cabin video display screen, remains constant when, forexample, the rear backup camera or other vehicular camera is operatedduring nighttime ambient lighting conditions, irrespective of theambient light level present during a particular reversing/drivingmaneuver. Thus, for example, the illumination level/display intensity ofthe displayed video images as seen by the driver who is reversing ordriving the vehicle in a dark, rural environment, where ambient lightingmay be low (for example, less than about five lux or less than about onelux or lower) may be consistent with displayed video images as seen bythe driver when the driver is reversing or driving the vehicle in anurban environment, where in addition to moonlight, area lighting fromthe likes of street lights and other lights may be present that adds tothe ambient light at the vehicle. For example, the display intensity mayhave a nominal or operating intensity of around or greater than about200 candelas per square meter, and the display intensity may beconsistently held within, for example, about 15 percent of its nominalor operating display intensity, or preferably within about 10 percent ofits nominal or operating display intensity or within about 5 percent ofits nominal or operating display intensity, irrespective of changes inthe ambient lighting level at or around the vehicle. The presentinvention thus provides consistency and uniformity of display imageintensity as viewed by the driver when driving/reversing the vehicleunder dark nighttime rural ambient lighting conditions or whendriving/reversing the vehicle under city or urban street lit higherambient lighting conditions. In accordance with the present invention,this is achieved without deterioration of the displayed and viewed videoimages, such as may otherwise occur when video noise is introduced suchas via utilization of gain-based video signal amplification.

The camera or sensor may comprise any suitable camera or sensor.Optionally, the camera may comprise a “smart camera” that includes theimaging sensor array and associated circuitry and image processingcircuitry and electrical connectors and the like as part of a cameramodule, such as by utilizing aspects of the vision systems described inInternational Publication Nos. WO 2013/081984 and/or WO 2013/081985,which are hereby incorporated herein by reference in their entireties.

The system includes an image processor operable to process image datacaptured by the camera or cameras, such as for detecting objects orother vehicles or pedestrians or the like in the field of view of one ormore of the cameras. For example, the image processor may comprise anEyeQ2 or EyeQ3 image processing chip available from Mobileye VisionTechnologies Ltd. of Jerusalem, Israel, and may include object detectionsoftware (such as the types described in U.S. Pat. Nos. 7,855,755;7,720,580 and/or 7,038,577, which are hereby incorporated herein byreference in their entireties), and may analyze image data to detectvehicles and/or other objects. Responsive to such image processing, andwhen an object or other vehicle is detected, the system may generate analert to the driver of the vehicle and/or may generate an overlay at thedisplayed image to highlight or enhance display of the detected objector vehicle, in order to enhance the driver's awareness of the detectedobject or vehicle or hazardous condition during a driving maneuver ofthe equipped vehicle.

The vehicle may include any type of sensor or sensors, such as imagingsensors or radar sensors or lidar sensors or ladar sensors or ultrasonicsensors or the like. The imaging sensor or camera may capture image datafor image processing and may comprise any suitable camera or sensingdevice, such as, for example, a two dimensional array of a plurality ofphotosensor elements arranged in at least 640 columns and 480 rows (atleast a 640×480 imaging array, such as a megapixel imaging array or thelike), with a respective lens focusing images onto respective portionsof the array. The photosensor array may comprise a plurality ofphotosensor elements arranged in a photosensor array having rows andcolumns. Preferably, the imaging array has at least 300,000 photosensorelements or pixels, more preferably at least 500,000 photosensorelements or pixels and more preferably at least 1 million photosensorelements or pixels. The imaging array may capture color image data, suchas via spectral filtering at the array, such as via an RGB (red, greenand blue) filter or via a red/red complement filter or such as via anRCC (red, clear, clear) filter or the like. The logic and controlcircuit of the imaging sensor may function in any known manner, and theimage processing and algorithmic processing may comprise any suitablemeans for processing the images and/or image data.

For example, the vision system and/or processing and/or camera and/orcircuitry may utilize aspects described in U.S. Pat. Nos. 7,005,974;5,760,962; 5,877,897; 5,796,094; 5,949,331; 6,222,447; 6,302,545;6,396,397; 6,498,620; 6,523,964; 6,611,202; 6,201,642; 6,690,268;6,717,610; 6,757,109; 6,802,617; 6,806,452; 6,822,563; 6,891,563;6,946,978; 7,859,565; 5,550,677; 5,670,935; 6,636,258; 7,145,519;7,161,616; 7,230,640; 7,248,283; 7,295,229; 7,301,466; 7,592,928;7,881,496; 7,720,580; 7,038,577; 6,882,287; 5,929,786 and/or 5,786,772,and/or International Publication Nos. WO 2011/028686; WO 2010/099416; WO2012/061567; WO 2012/068331; WO 2012/075250; WO 2012/103193; WO2012/0116043; WO 2012/0145313; WO 2012/0145501; WO 2012/145818; WO2012/145822; WO 2012/158167; WO 2012/075250; WO 2012/0116043; WO2012/0145501; WO 2012/154919; WO 2013/019707; WO 2013/016409; WO2013/019795; WO 2013/067083; WO 2013/070539; WO 2013/043661; WO2013/048994; WO 2013/063014, WO 2013/081984; WO 2013/081985; WO2013/074604; WO 2013/086249; WO 2013/103548; WO 2013/109869; WO2013/123161; WO 2013/126715; WO 2013/043661 and/or WO 2013/158592,and/or U.S. patent application Ser. No. 14/268,169, filed May 2, 2014,and published Nov. 6, 2014 as U.S. Publication No. US-2014-032772; Ser.No. 14/264,443, filed Apr. 29, 2014, and published Oct. 30, 2014 as U.S.Publication No. US-2014-0320636; Ser. No. 14/354,675, filed Apr. 28,2014, now U.S. Pat. No. 9,580,013; Ser. No. 14/248,602, filed Apr. 9,2014, now U.S. Pat. No. 9,327,693; Ser. No. 14/242,038, filed Apr. 1,2014, now U.S. Pat. No. 9,487,159; Ser. No. 14/229,061, filed Mar. 28,2014, and published Oct. 2, 2014 as U.S. Publication No.US-2014-0293042; Ser. No. 14/343,937, filed Mar. 10, 2014, now U.S. Pat.No. 9,681,062; Ser. No. 14/343,936, filed Mar. 10, 2014, and publishedAug. 7, 2014 as U.S. Publication No. US-2014-0218535; Ser. No.14/195,135, filed Mar. 3, 2014, now U.S. Pat. No. 9,688,200; Ser. No.14/195,136, filed Mar. 3, 2014, and published Sep. 4, 2014 as U.S.Publication No. US-2014-0247355; Ser. No. 14/191,512, filed Feb. 27,2014, and published Sep. 4, 2014 as U.S. Publication No.US-2014-0247352; Ser. No. 14/183,613, filed Feb. 19, 2014, now U.S. Pat.No. 9,445,057; Ser. No. 14/169,329, filed Jan. 31, 2014, and publishedAug. 7, 2014 as U.S. Publication No. US-2014-0218529; Ser. No.14/169,328, filed Jan. 31, 2014, now U.S. Pat. No. 9,092,986; Ser. No.14/163,325, filed Jan. 24, 2014, and published Jul. 31, 2014 as U.S.Publication No. US-2014-0211009; Ser. No. 14/159,772, filed Jan. 21,2014, now U.S. Pat. No. 9,068,390; Ser. No. 14/107,624, filed Dec. 16,2013, now U.S. Pat. No. 9,140,789; Ser. No. 14/102,981, filed Dec. 11,2013, now U.S. Pat. No. 9,558,409; Ser. No. 14/102,980, filed Dec. 11,2013, and published Jun. 19, 2014 as U.S. Publication No.US-2014-0168437; Ser. No. 14/098,817, filed Dec. 6, 2013, and publishedJun. 19, 2014 as U.S. Publication No. US-2014-0168415; Ser. No.14/097,581, filed Dec. 5, 2013, now U.S. Pat. No. 9,481,301; Ser. No.14/093,981, filed Dec. 2, 2013, now U.S. Pat. No. 8,917,169; Ser. No.14/093,980, filed Dec. 2, 2013, and published Jun. 5, 2014 as U.S.Publication No. US-2014-0152825; Ser. No. 14/082,573, filed Nov. 18,2013, now U.S. Pat. No. 9,743,002; Ser. No. 14/082,574, filed Nov. 18,2013, now U.S. Pat. No. 9,307,640; Ser. No. 14/082,575, filed Nov. 18,2013, now U.S. Pat. No. 9,090,234; Ser. No. 14/082,577, filed Nov. 18,2013, now U.S. Pat. No. 8,818,042; Ser. No. 14/071,086, filed Nov. 4,2013, now U.S. Pat. No. 8,886,401; Ser. No. 14/076,524, filed Nov. 11,2013, now U.S. Pat. No. 9,077,962; Ser. No. 14/052,945, filed Oct. 14,2013, now U.S. Pat. No. 9,707,896; Ser. No. 14/046,174, filed Oct. 4,2013, now U.S. Pat. No. 9,723,272; Ser. No. 14/016,790, filed Oct. 3,2013, now U.S. Pat. No. 9,761,142; Ser. No. 14/036,723, filed Sep. 25,2013, now U.S. Pat. No. 9,446,713; Ser. No. 14/016,790, filed Sep. 3,2013, now U.S. Pat. No. 9,761,142; Ser. No. 14/001,272, filed Aug. 23,2013, now U.S. Pat. No. 9,233,641; Ser. No. 13/970,868, filed Aug. 20,2013, now U.S. Pat. No. 9,365,162; Ser. No. 13/964,134, filed Aug. 12,2013, now U.S. Pat. No. 9,340,227; Ser. No. 13/942,758, filed Jul. 16,2013, and published on Jan. 23, 2014 as U.S. Publication No.US-2014-0025240; Ser. No. 13/942,753, filed Jul. 16, 2013, and publishedJan. 30, 2014 as U.S. Publication No. US-2014-0028852; Ser. No.13/927,680, filed Jun. 26, 2013, and published Jan. 2, 2014 as U.S.Publication No. US-2014-0005907; Ser. No. 13/916,051, filed Jun. 12,2013, now U.S. Pat. No. 9,077,098; Ser. No. 13/894,870, filed May 15,2013, and published Nov. 28, 2013 as U.S. Publication No.US-2013-0314503; Ser. No. 13/887,724, filed May 6, 2013, now U.S. Pat.No. 9,670,895; Ser. No. 13/852,190, filed Mar. 28, 2013, and publishedAug. 29, 2013 as U.S. Patent Publication No. US-2013/0222593; Ser. No.13/851,378, filed Mar. 27, 2013, now U.S. Pat. No. 9,319,637; Ser. No.13/848,796, filed Mar. 22, 2012, and published Oct. 24, 2013 as U.S.Publication No. US-2013-0278769; Ser. No. 13/847,815, filed Mar. 20,2013, and published Oct. 31, 2013 as U.S. Publication No.US-2013-0286193; Ser. No. 13/800,697, filed Mar. 13, 2013, and publishedOct. 3, 2013 as U.S. Publication No. US-2013-0258077; Ser. No.13/785,099, filed Mar. 5, 2013, now U.S. Pat. No. 9,565,342; Ser. No.13/779,881, filed Feb. 28, 2013, now U.S. Pat. No. 8,694,224; Ser. No.13/774,317, filed Feb. 22, 2013, now U.S. Pat. No. 9,269,263; Ser. No.13/774,315, filed Feb. 22, 2013, and published Aug. 22, 2013 as U.S.Publication No. US-2013-0215271; Ser. No. 13/681,963, filed Nov. 20,2012, now U.S. Pat. No. 9,264,673; Ser. No. 13/660,306, filed Oct. 25,2012, now U.S. Pat. No. 9,146,898; Ser. No. 13/653,577, filed Oct. 17,2012, now U.S. Pat. No. 9,174,574; and/or Ser. No. 13/534,657, filedJun. 27, 2012, and published Jan. 3, 2013 as U.S. Publication No.US-2013-0002873, and/or U.S. provisional applications, Ser. No.61/981,938, filed Apr. 21, 2014; Ser. No. 61/981,937, filed Apr. 21,2014; Ser. No. 61/977,941, filed Apr. 10, 2014; Ser. No. 61/977,940.filed Apr. 10, 2014; Ser. No. 61/977,929, filed Apr. 10, 2014; Ser. No.61/977,928, filed Apr. 10, 2014; Ser. No. 61/973,922, filed Apr. 2,2014; Ser. No. 61/972,708, filed Mar. 31, 2014; Ser. No. 61/972,707,filed Mar. 31, 2014; Ser. No. 61/969,474, filed Mar. 24, 2014; Ser. No.61/955,831, filed Mar. 20, 2014; Ser. No. 61/953,970, filed Mar. 17,2014; Ser. No. 61/952,335, filed Mar. 13, 2014; Ser. No. 61/952,334,filed Mar. 13, 2014; Ser. No. 61/950,261, filed Mar. 10, 2014; Ser. No.61/950,261, filed Mar. 10, 2014; Ser. No. 61/947,638, filed Mar. 4,2014; Ser. No. 61/947,053, filed Mar. 3, 2014; Ser. No. 61/941,568,filed Feb. 19, 2014; Ser. No. 61/935,485, filed Feb. 4, 2014; Ser. No.61/935,057, filed Feb. 3, 2014; Ser. No. 61/935,056, filed Feb. 3, 2014;Ser. No. 61/935,055, filed Feb. 3, 2014; Ser. 61/931,811, filed Jan. 27,2014; Ser. No. 61/919,129, filed Dec. 20, 2013; Ser. No. 61/919,130,filed Dec. 20, 2013; Ser. No. 61/919,131, filed Dec. 20, 2013; Ser. No.61/919,147, filed Dec. 20, 2013; Ser. No. 61/919,138, filed Dec. 20,2013, Ser. No. 61/919,133, filed Dec. 20, 2013; Ser. No. 61/918,290,filed Dec. 19, 2013; Ser. No. 61/915,218, filed Dec. 12, 2013; Ser. No.61/912,146, filed Dec. 5, 2013; Ser. No. 61/911,666, filed Dec. 4, 2013;Ser. No. 61/911,665, filed Dec. 4, 2013; Ser. No. 61/905,461, filed Nov.18, 2013; Ser. No. 61/905,462, filed Nov. 18, 2013; Ser. No. 61/901,127,filed Nov. 7, 2013; Ser. No. 61/895,610, filed Oct. 25, 2013; Ser. No.61/895,609, filed Oct. 25, 2013; Ser. No. 61/879,837, filed Sep. 19,2013; Ser. No. 61/879,835, filed Sep. 19, 2013; Ser. No. 61/878,877,filed Sep. 17, 2013; Ser. No. 61/875,351, filed Sep. 9, 2013; Ser. No.61/869,195, filed. Aug. 23, 2013; Ser. No. 61/864,835, filed Aug. 12,2013; Ser. No. 61/864,836, filed Aug. 12, 2013; Ser. No. 61/864,837,filed Aug. 12, 2013; Ser. No. 61/864,838, filed Aug. 12, 2013; Ser. No.61/856,843, filed Jul. 22, 2013, Ser. No. 61/845,061, filed Jul. 11,2013; Ser. No. 61/844,630, filed Jul. 10, 2013; Ser. No. 61/844,173,filed Jul. 9, 2013; Ser. No. 61/844,171, filed Jul. 9, 2013; Ser. No.61/842,644, filed Jul. 3, 2013; Ser. No. 61/840,542, filed Jun. 28,2013; Ser. No. 61/838,619, filed Jun. 24, 2013; Ser. No. 61/838,621,filed Jun. 24, 2013; Ser. No. 61/837,955, filed Jun. 21, 2013; Ser. No.61/836,900, filed Jun. 19, 2013; Ser. No. 61/836,380, filed Jun. 18,2013; Ser. No. 61/833,080, filed Jun. 10, 2013; Ser. No. 61/830,377,filed Jun. 3, 2013; Ser. No. 61/825,752, filed May 21, 2013; Ser. No.61/825,753, filed May 21, 2013; Ser. No. 61/823,648, filed May 15, 2013;Ser. No. 61/823,644, filed May 15, 2013; Ser. No. 61/821,922, filed May10, 2013; and/or Ser. No. 61/819,835, filed May 6, 2013, which are allhereby incorporated herein by reference in their entireties. The systemmay communicate with other communication systems via any suitable means,such as by utilizing aspects of the systems described in InternationalPublication Nos. WO/2010/144900; WO 2013/043661 and/or WO 2013/081985,and/or U.S. patent application Ser. No. 13/202,005, filed Aug. 17, 2011,now U.S. Pat. No. 9,126,525, which are hereby incorporated herein byreference in their entireties.

The imaging device and control and image processor and any associatedillumination source, if applicable, may comprise any suitablecomponents, and may utilize aspects of the cameras and vision systemsdescribed in U.S. Pat. Nos. 5,550,677; 5,877,897; 6,498,620; 5,670,935;5,796,094; 6,396,397; 6,806,452; 6,690,268; 7,005,974; 7,937,667;7,123,168; 7,004,606; 6,946,978; 7,038,577; 6,353,392; 6,320,176;6,313,454 and/or 6,824,281, and/or International Publication Nos. WO2010/099416; WO 2011/028686 and/or WO 2013/016409, and/or U.S. Pat.Publication No. US 2010-0020170, and/or U.S. patent application Ser. No.13/534,657, filed Jun. 27, 2012, and published Jan. 3, 2013 as U.S.Publication No. US-2013-0002873, which are all hereby incorporatedherein by reference in their entireties. The camera or cameras maycomprise any suitable cameras or imaging sensors or camera modules, andmay utilize aspects of the cameras or sensors described in U.S.Publication No. US-2009-0244361 and/or U.S. patent application Ser. No.13/260,400, filed Sep. 26, 2011, now U.S. Pat. No. 8,542,451, and/orU.S. Pat. Nos. 7,965,336 and/or 7,480,149, which are hereby incorporatedherein by reference in their entireties. The imaging array sensor maycomprise any suitable sensor, and may utilize various imaging sensors orimaging array sensors or cameras or the like, such as a CMOS imagingarray sensor, a CCD sensor or other sensors or the like, such as thetypes described in U.S. Pat. Nos. 5,550,677; 5,670,935; 5,760,962;5,715,093; 5,877,897; 6,922,292; 6,757,109; 6,717,610; 6,590,719;6,201,642; 6,498,620; 5,796,094; 6,097,023; 6,320,176; 6,559,435;6,831,261; 6,806,452; 6,396,397; 6,822,563; 6,946,978; 7,339,149;7,038,577; 7,004,606; 7,720,580 and/or 7,965,336, and/or InternationalPublication Nos. WO/2009/036176 and/or WO/2009/046268, which are allhereby incorporated herein by reference in their entireties.

The camera module and circuit chip or board and imaging sensor may beimplemented and operated in connection with various vehicularvision-based systems, and/or may be operable utilizing the principles ofsuch other vehicular systems, such as a vehicle headlamp control system,such as the type disclosed in U.S. Pat. Nos. 5,796,094; 6,097,023;6,320,176; 6,559,435; 6,831,261; 7,004,606; 7,339,149 and/or 7,526,103,which are all hereby incorporated herein by reference in theirentireties, a rain sensor, such as the types disclosed in commonlyassigned U.S. Pat. Nos. 6,353,392; 6,313,454; 6,320,176 and/or7,480,149, which are hereby incorporated herein by reference in theirentireties, a vehicle vision system, such as a forwardly, sidewardly orrearwardly directed vehicle vision system utilizing principles disclosedin U.S. Pat. Nos. 5,550,677; 5,670,935; 5,760,962; 5,877,897; 5,949,331;6,222,447; 6,302,545; 6,396,397; 6,498,620; 6,523,964; 6,611,202;6,201,642; 6,690,268; 6,717,610; 6,757,109; 6,802,617; 6,806,452;6,822,563; 6,891,563; 6,946,978 and/or 7,859,565, which are all herebyincorporated herein by reference in their entireties, a trailer hitchingaid or tow check system, such as the type disclosed in U.S. Pat. No.7,005,974, which is hereby incorporated herein by reference in itsentirety, a reverse or sideward imaging system, such as for a lanechange assistance system or lane departure warning system or for a blindspot or object detection system, such as imaging or detection systems ofthe types disclosed in U.S. Pat. Nos. 7,881,496; 7,720,580; 7,038,577;5,929,786 and/or 5,786,772, and/or U.S. provisional applications, Ser.No. 60/628,709, filed Nov. 17, 2004; Ser. No. 60/614,644, filed Sep. 30,2004; Ser. No. 60/618,686, filed Oct. 14, 2004; Ser. No. 60/638,687,filed Dec. 23, 2004, which are hereby incorporated herein by referencein their entireties, a video device for internal cabin surveillanceand/or video telephone function, such as disclosed in U.S. Pat. Nos.5,760,962; 5,877,897; 6,690,268 and/or 7,370,983, and/or U.S.Publication No. US-2006-0050018, which are hereby incorporated herein byreference in their entireties, a traffic sign recognition system, asystem for determining a distance to a leading or trailing vehicle orobject, such as a system utilizing the principles disclosed in U.S. Pat.Nos. 6,396,397 and/or 7,123,168, which are hereby incorporated herein byreference in their entireties, and/or the like.

Optionally, the circuit board or chip may include circuitry for theimaging array sensor and or other electronic accessories or features,such as by utilizing compass-on-a-chip or EC driver-on-a-chip technologyand aspects such as described in U.S. Pat. No. 7,255,451 and/or U.S.Pat. No. 7,480,149; and/or U.S. Publication No. US-2006-0061008 and/orU.S. patent application Ser. No. 12/578,732, filed Oct. 14, 2009, nowU.S. Pat. No. 9,487,144, which are hereby incorporated herein byreference in their entireties.

Optionally, the vision system may include a display for displayingimages captured by one or more of the imaging sensors for viewing by thedriver of the vehicle while the driver is normally operating thevehicle. Optionally, for example, the vision system may include a videodisplay device disposed at or in the interior rearview mirror assemblyof the vehicle, such as by utilizing aspects of the video mirror displaysystems described in U.S. Pat. No. 6,690,268 and/or U.S. patentapplication Ser. No. 13/333,337, filed Dec. 21, 2011, now U.S. Pat. No.9,264,672, which are hereby incorporated herein by reference in theirentireties. The video mirror display may comprise any suitable devicesand systems and optionally may utilize aspects of the compass displaysystems described in U.S. Pat. Nos. 7,370,983; 7,329,013; 7,308,341;7,289,037; 7,249,860; 7,004,593; 4,546,551; 5,699,044; 4,953,305;5,576,687; 5,632,092; 5,677,851; 5,708,410; 5,737,226; 5,802,727;5,878,370; 6,087,953; 6,173,508; 6,222,460; 6,513,252 and/or 6,642,851,and/or European patent application, published Oct. 11, 2000 underPublication No. EP 0 1043566, and/or U.S. Publication No.US-2006-0061008, which are all hereby incorporated herein by referencein their entireties. Optionally, the video mirror display screen ordevice may be operable to display images captured by a rearward viewingcamera of the vehicle during a reversing maneuver of the vehicle (suchas responsive to the vehicle gear actuator being placed in a reversegear position or the like) to assist the driver in backing up thevehicle, and optionally may be operable to display the compass headingor directional heading character or icon when the vehicle is notundertaking a reversing maneuver, such as when the vehicle is beingdriven in a forward direction along a road (such as by utilizing aspectsof the display system described in International Publication No. WO2012/051500, which is hereby incorporated herein by reference in itsentirety).

Optionally, the vision system (utilizing the forward facing camera and arearward facing camera and other cameras disposed at the vehicle withexterior fields of view) may be part of or may provide a display of atop-down view or birds-eye view system of the vehicle or a surround viewat the vehicle, such as by utilizing aspects of the vision systemsdescribed in International Publication Nos. WO 2010/099416; WO2011/028686; WO2012/075250; WO 2013/019795; WO 2012/075250; WO2012/145822; WO 2013/081985; WO 2013/086249 and/or WO 2013/109869,and/or U.S. patent application Ser. No. 13/333,337, filed Dec. 21, 2011,now U.S. Pat. No. 9,264,672, which are hereby incorporated herein byreference in their entireties.

Optionally, a video mirror display may be disposed rearward of andbehind the reflective element assembly and may comprise a display suchas the types disclosed in U.S. Pat. Nos. 5,530,240; 6,329,925;7,855,755; 7,626,749; 7,581,859; 7,446,650; 7,370,983; 7,338,177;7,274,501; 7,255,451; 7,195,381; 7,184,190; 5,668,663; 5,724,187 and/or6,690,268, and/or in U.S. Publication Nos. US-2006-0061008 and/orUS-2006-0050018, which are all hereby incorporated herein by referencein their entireties. The display is viewable through the reflectiveelement when the display is activated to display information. Thedisplay element may be any type of display element, such as a vacuumfluorescent (VF) display element, a light emitting diode (LED) displayelement, such as an organic light emitting diode (OLED) or an inorganiclight emitting diode, an electroluminescent (EL) display element, aliquid crystal display (LCD) element, a video screen display element orbacklit thin film transistor (TFT) display element or the like, and maybe operable to display various information (as discrete characters,icons or the like, or in a multi-pixel manner) to the driver of thevehicle, such as passenger side inflatable restraint (PSIR) information,tire pressure status, and/or the like. The mirror assembly and/ordisplay may utilize aspects described in U.S. Pat. Nos. 7,184,190;7,255,451; 7,446,924 and/or 7,338,177, which are all hereby incorporatedherein by reference in their entireties. The thicknesses and materialsof the coatings on the substrates of the reflective element may beselected to provide a desired color or tint to the mirror reflectiveelement, such as a blue colored reflector, such as is known in the artand such as described in U.S. Pat. Nos. 5,910,854; 6,420,036 and/or7,274,501, which are hereby incorporated herein by reference in theirentireties.

Optionally, the display or displays and any associated user inputs maybe associated with various accessories or systems, such as, for example,a tire pressure monitoring system or a passenger air bag status or agarage door opening system or a telematics system or any other accessoryor system of the mirror assembly or of the vehicle or of an accessorymodule or console of the vehicle, such as an accessory module or consoleof the types described in U.S. Pat. Nos. 7,289,037; 6,877,888;6,824,281; 6,690,268; 6,672,744; 6,386,742 and 6,124,886, and/or U.S.Publication No. US-2006-0050018, which are hereby incorporated herein byreference in their entireties.

Changes and modifications in the specifically described embodiments canbe carried out without departing from the principles of the invention,which is intended to be limited only by the scope of the appendedclaims, as interpreted according to the principles of patent lawincluding the doctrine of equivalents.

1. A vehicular multi-camera vision system, said vehicular multi-cameravision system comprising: a plurality of cameras disposed at a vehicle,each having a field of view exterior of the vehicle and each comprisinga two dimensional array of a plurality of photosensing elements; acontrol comprising an image processor operable to process image datacaptured by said cameras; said cameras comprising a rear-mounted cameradisposed at a rear portion of the vehicle and having a field of view atleast rearward of the vehicle; said cameras comprising a front-mountedcamera disposed at a front portion of the vehicle and having a field ofview at least forward of the vehicle; said cameras comprising a driverside-mounted camera disposed at a driver side portion of the vehicle andhaving a field of view at least sideward of the vehicle; said camerascomprising a passenger side-mounted camera disposed at a passenger sideportion of the vehicle and having a field of view at least sideward ofthe vehicle; a display device viewable by a driver of the vehicle,wherein said display device comprising a video display screen; whereinsaid control is operable to control a display intensity of video imagesdisplayed by said video display screen; and wherein, responsive to adetermination of a reduction in exterior ambient light level within thefield of view of at least one of said cameras, said control holdsdisplay intensity of video images displayed by said video display screento within 15 percent of the display intensity that was displayed beforethe determination of the reduction in exterior ambient light level by(a) adjusting an exposure time for image data capture by at least someof said cameras and by (b) at least one of (i) adjusting a frame rate ofimage data capture by at least one of said cameras and (ii) adjusting again of at least one of said cameras.
 2. The vehicular multi-cameravision system of claim 1, wherein, responsive to a determination of areduction in exterior ambient light level within the field of view of atleast one of said cameras, said control adjusts an exposure time forimage data capture by at least some of said cameras to hold displayintensity of video images displayed by said video display screen towithin 10 percent of the display intensity that was displayed before thedetermination of the reduction in exterior ambient light level.
 3. Thevehicular multi-camera vision system of claim 1, wherein, responsive tothe determination of a reduction in exterior ambient light level withinthe field of view of at least one of said cameras, said controlincreases the exposure time of at least one of said cameras.
 4. Thevehicular multi-camera vision system of claim 3, wherein, responsive tothe determination of reduction in exterior ambient light level, saidcontrol increases the exposure time of said one of said cameras to amultiple of the exposure time used at higher ambient lighting levels. 5.The vehicular multi-camera vision system of claim 1, wherein saidcontrol controls at least one of said cameras to provide a consistentdisplay intensity of displayed video images irrespective of whether thevehicle is operated at nighttime in a rural driving environment or acity driving environment.
 6. The vehicular multi-camera vision system ofclaim 1, wherein said control is operable to control an analog gain ofat least one of said cameras.
 7. The vehicular multi-camera visionsystem of claim 1, wherein said control adjusts (i) an exposure time forimage data capture by at least some of said cameras and (ii) a framerate of image data capture by at least one of said cameras.
 8. Thevehicular multi-camera vision system of claim 7, wherein, responsive toa determination of a reduction in exterior ambient light level withinthe field of view of at least one of said cameras, said control adjuststhe exposure time for image data capture by at least some of saidcameras to a longer exposure time and adjusts their frame rate to aslower frame rate.
 9. The vehicular multi-camera vision system of claim1, wherein said control is operable to decouple color processing andluminance processing of image data captured by at least some of saidcameras to improve detail visibility.
 10. The vehicular multi-cameravision system of claim 1, wherein said vehicular multi-camera visionsystem comprises a bird's eye-view vision system.
 11. The vehicularmulti-camera vision system of claim 1, wherein said video display screenis operable to display video images, as viewed by a driver operating thevehicle, with a display intensity greater than 200 candelas per squaremeter.
 12. The vehicular multi-camera vision system of claim 11, whereinsaid control is operable to control the illumination level in adisplayed image derived, at least in part, from image data captured byat least one of said cameras.
 13. A vehicular multi-camera visionsystem, said vehicular multi-camera vision system comprising: aplurality of cameras disposed at a vehicle, each having a field of viewexterior of the vehicle and each comprising a two dimensional array of aplurality of photosensing elements; a control comprising an imageprocessor operable to process image data captured by said cameras; saidcameras comprising a rear-mounted camera disposed at a rear portion ofthe vehicle and having a field of view at least rearward of the vehicle;said cameras comprising a front-mounted camera disposed at a frontportion of the vehicle and having a field of view at least forward ofthe vehicle; said cameras comprising a driver side-mounted cameradisposed at a driver side portion of the vehicle and having a field ofview at least sideward of the vehicle; said cameras comprising apassenger side-mounted camera disposed at a passenger side portion ofthe vehicle and having a field of view at least sideward of the vehicle;a display device viewable by a driver of the vehicle, wherein saiddisplay device comprising a video display screen; wherein said vehicularmulti-camera vision system comprises a bird's eye-view vision system;wherein said video display screen is operable to display video images,as viewed by a driver operating the vehicle, with a display intensitygreater than 200 candelas per square meter; wherein said control isoperable to control a display intensity of video images displayed bysaid video display screen; and wherein, responsive to a determination ofa reduction in exterior ambient light level within the field of view ofat least one of said cameras, said control adjusts the exposure time forimage data capture by at least some of said cameras to a longer exposuretime and adjusts their frame rate to a slower frame rate in order tohold display intensity of video images displayed by said video displayscreen to within 15 percent of the display intensity that was displayedbefore the determination of the reduction in exterior ambient lightlevel.
 14. The vehicular multi-camera vision system of claim 13, whereinsaid control controls at least one of said cameras to provide aconsistent display intensity of displayed video images irrespective ofwhether the vehicle is operated at nighttime in a rural drivingenvironment or a city driving environment.
 15. The vehicularmulti-camera vision system of claim 14, wherein said control is operableto control an analog gain of at least one of said cameras.
 16. Avehicular multi-camera vision system, said vehicular multi-camera visionsystem comprising: a plurality of cameras disposed at a vehicle, eachhaving a field of view exterior of the vehicle and each comprising a twodimensional array of a plurality of photosensing elements; a controlcomprising an image processor operable to process image data captured bysaid cameras; said cameras comprising a rear-mounted camera disposed ata rear portion of the vehicle and having a field of view at leastrearward of the vehicle; said cameras comprising a front-mounted cameradisposed at a front portion of the vehicle and having a field of view atleast forward of the vehicle; said cameras comprising a driverside-mounted camera disposed at a driver side portion of the vehicle andhaving a field of view at least sideward of the vehicle; said camerascomprising a passenger side-mounted camera disposed at a passenger sideportion of the vehicle and having a field of view at least sideward ofthe vehicle; a display device viewable by a driver of the vehicle,wherein said display device comprising a video display screen; whereinsaid control is operable to control a display intensity of video imagesdisplayed by said video display screen; and wherein, responsive to adetermination of a reduction in exterior ambient light level within thefield of view of at least one of said cameras, said control holdsdisplay intensity of video images displayed by said video display screento within 15 percent of the display intensity that was displayed beforethe determination of the reduction in exterior ambient light level byincreasing an exposure time for image data capture by at least one ofsaid cameras and by decreasing a frame rate of image data capture bysaid at least one of said cameras.
 17. The vehicular multi-camera visionsystem of claim 16, wherein the frame rate of image data capture by saidat least one of said cameras decreases from 30 frames/second.
 18. Thevehicular multi-camera vision system of claim 17, wherein the frame rateof image data capture by said at least one of said cameras decreases tono lower than 15 frames/second.
 19. The vehicular multi-camera visionsystem of claim 16, wherein said vehicular multi-camera vision systemcomprises a bird's eye-view vision system.
 20. The vehicularmulti-camera vision system of claim 19, wherein said video displayscreen is operable to display video images, as viewed by a driveroperating the vehicle, with a display intensity greater than 200candelas per square meter.